When bending a metal work piece, such as a strip or wire, heat is generated at the site of the bend. It is known that if the bend is performed at very high speed, fracturing that would normally occur does not occur. For example, it has been found that if a bending operation is performed in a sufficiently short time, e.g., about 3.9 to about 1.5 milliseconds or less, work hardening does not have sufficient time to occur and there is no fracturing of the material as a result. In other words, if the time period of the bending operation is less than the stress versus thermal diffusivity time constant for the particular metal, no fracturing of the metal will occur during bending. It is believed that during bending a sufficiently high temperature is developed at the site of deformation so that the crystal planes of the metal tend to slip as though the material were fully annealed.
Most prior art stamping and forming machines do not provide the speeds necessary for the successful forming of relatively hard materials, e.g., Paliney No. 7 in its full hard condition. An apparatus has been constructed and tested that demonstrates that such forming is easily achievable. More particularly, in U.S. Pat. No. 5,606,888, a method is disclosed for performing a forming operation on a strip of relatively hard material which patent is hereby incorporated herein by reference. The method of the invention includes the steps of providing tooling having a first tool and a second tool that are matable with one another for performing a forming operation, e.g., a die and punch. A stamping and forming machine is provided having the first and second tools operatively assembled therein. In this construction, the first tool is arranged to undergo movement toward the second tool and then into mated engagement with the second tool, followed by movement away from the second tool out of mated engagement. In operation, a strip of relatively hard material is placed between the first and second tools and the stamping and forming machine is operated so that the movement causes the first tool to move toward the second tool to a first position and engagement with the strip of relatively hard material. The tool is then further moved to a second position in mated engagement with the second tool thereby completing the forming operation. Significantly, the first tool moves from the first position to the second position at a rate of speed sufficiently fast so that the forming operation is completed without cracking the strip of relatively hard material.
In U.S. Pat. No. 5,606,888, an audio speaker is disclosed for use as a transducer to drive the first tool (forming tool) into mating engagement with the second tool (die) to perform a forming operation on a strip of relatively hard material. While an audio speaker is suitable for applying the teachings of that patent to very small parts, a high speed stamping and forming machine having a capability of performing forming operations in the preferred time period of about 0.15 milliseconds is far more desirable and suitable for larger parts such as electrical contacts or electrical connectors.
Consequently, there is a need for a mechanism that is adapted to be placed among the tools operating in a conventional stamping and forming press, running at conventional speeds, and that provides the necessary tool closure rate to assure that forming occurs within a relatively short time period.